Measurement of the particle movement in the fountain region of a Wurster type bed

A non-intrusive technique to follow single particles in the fountain region of a spouted bed with draft tube, the Wurster coater, is developed and tested. Compared to other techniques found in literature, the measurement technique presented here is easy to handle, inexpensive and suitable for particles with a diameter down to 500 μm. The measurements are performed in a laboratory scale Wurster bed constructed of Plexiglas to allow optical access to the flow. A small quantity of the particles in the bed are marked with fluorescence. A UV lamp is used to excite the fluorescence and the marked particles are followed with a high-speed video camera equipped with an optical filter. A single marked particle in the fountain can be followed in 5–30 images in sequence at a frame rate of 125 fps. The particle position and velocity are calculated. The distribution of the particle trajectories maximum height is studied for different particle loading, jet air velocity and position of the Wurster tube. The technique can be used for the characterization of differences in process dynamics due to different operating conditions.